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HPOD
Theory of Operation
3.2 SSPA Module
The amplifier module performs the core function of the unit. An isolator is at the RF
input to ensure good VSWR. The RF signal then passes through an input sample port
and on to an electronically controlled attenuator that adjusts the overall attenuation
according to the user input. After some amplification, a second attenuator is
automatically controlled via a look-up table to maintain the amplifier gain at a constant
level over temperature variations.
The RF signal is then amplified by a multi-stage design that utilizes proprietary
combining techniques to meet the rated power requirements. The output circuitry
contains a coupler to provide a sampled signal for monitoring purposes. A power
detector circuit also is included and the reading can be accessed via remote
communication. A high power circulator and load is located at the output to provide
good VSWR and protection from external mismatch.
3.3 Cooling System
The SSPA unit contains a robust heat sink and thermal design to maintain a low operating
temperature. Two temperature controlled fans, which are monitored by the M&C board,
draw cool outside air in across the power supply and specialized heat sink and exhaust
the warmer air out the bottom of the unit. The amplifier module temperature is
monitored, and if for any reason the amplifier temperature exceeds a safe preset limit, the
amplifier module supply is shut down to protect the unit from thermal failure.
3.4 Monitor and Control (M&C)
The unit includes a microprocessor based system that provides monitoring and control of
the essential parameters of the unit. The user interfaces with the unit through the M&C
system via the remote control/discrete communications port. The unit is capable of either
RS-232 or RS-485 remote communication. A discrete mute control and relay status
output is also available. The M&C system monitors the fan speed, unit temperature, all
power supply voltages, power transistor currents, output power, etc. Should a critical
monitored parameter fail, the unit will mute the RF signal and report a fault. The details
of the fault can be accessed via remote communication.
The M&C is also capable of acting as a controller in certain 1:1 or 1:2 redundant systems.
When configured as the back-up SSPA in such a system, it communicates with the other
SSPA(s) and toggles the waveguide switches as necessary.
3–3
Revision 2
MN/HPOD.IOM
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